headphone amp question

I have an Antique Sound Labs MG Head OTL Mark II headphone amp and Sennheiser 580 headphones in my main system. It seems that the volume in my library (another room) is too much for my wife so I am looking to add another headphone amplifier to that room. Should I buy another ASL headphone amp or upgrade to the next level? I plan on keeping the Senns. I like them alot. What other candidates should I consider? I know there is another headphone only site, but I have grown accustomed and comfortable with the advice from Audiogon. Thanks for your guidance. And, by the way, thanks for years of advice and entertainment from this website.